Hebe de Bonafini, the leader of the Mothers of Plaza de Mayo, an association of Argentine mothers whose children disappeared under the country's military dictatorship, was among those waiting to pay their respects.

"Certainly the scenery here doesn't show the low popularity that this government has had for the last couple of years," Al Jazeera's correspondent said.

"This is also an example of how important Kirchner was in Argentine politics."

Chavez mourns

Kirchner, 60, who was succeeded by his wife as president in 2007, had been expected to run in the 2011 presidential election.

He is widely credited by supporters for helping to lift the country out of the slump which followed the country's 2001 to 2002 financial crisis.

"After General Peron, he's the best president we ever had," said Estela Orellano, a 56-year-old housewife, referring to the former leader whose figure still looms large in the nation's political life.

Many people queued for hours to pay their respects to the president [Reuters]

A member of the dominant Peronist party, Kirchner built strong alliances as president that won him solid backing while also steering the party to the left and courting regional leftists such as Hugo Chavez, the president of Venezuela.

Posters carrying the slogan "Nestor forever, hang in there Cristina" have appeared across the capital.

Bolivia's President Evo Morales, the first foreign leader to arrive, said he felt orphaned by the death of an "irreplaceable" man who guided him through difficult times and inspired South America.

Brazilian President Luiz Inacio Lula da Silva announced he, too, was flying to Buenos Aires on Thursday after canceling all his appointments and declaring three days of mourning.

Others in Buenos Aires to attend the funeral included presidents Rafael Correa of Ecuador, Juan Manuel Santos of Colombia, Sebastian Pinera of Chile, Mujica of Uruguay, Fernando Lugo of Paraguay and Hugo Chavez of Venezuela.

Opposition leaders paid tribute to Kirchner's political savvy, but they may feel emboldened by his sudden departure.

Fernandez's approval ratings are around 35 per cent, too low to suggest she could win a first-round victory in the 2011 vote.

Argentina, a leading agricultural exporter, has benefited from a boom in commodities prices since its economic debacle nine years ago that plunged millions of Argentines into poverty and prompted a massive default and sharp devaluation in its curreny.

Mourning will continue until Friday, with all football games cancelled until next week.